Photoconductive layer comprising a selenium compound and a solid hydrophobic metal salt of a fatty acid



Jan. 13, 1970 R. J. JOSEPH 3,489,560 PHOTOGONDUCTIVE- LAYER' COMPRISINGA SELENIUM COMPOUND AND A SOLID HYDROPHOBIC METAL SALT OF A FATTY ACIDFiled Nov. 14. 1966 INVENTOR. ROBERT J. JOSEPH United States Patent 3489,560 PHOTOCONDUCTIVE LAYER COMPRISING A SE- LENIUM COMPOUND AND ASOLID HYDRO- PHOBIC METAL SALT OF A FATTY ACID Robert John Joseph,Penfield, N.Y., assignor to Xerox Corporation, Rochester, N.Y., acorporation of New York Filed Nov. 14, 1966, Ser. No. 594,074 Int. Cl.G03g 5/08, 13/00 U.S. Cl. 96-15 8 Claims ABSTRACT OF THE DISCLOSURE Anelectrophotographic plate is produced by co-evaporation of a seleniummaterial and a solid hydrophobic metal salt of a fatty acid onto aconductive substrate. The plate may be used in conventionalelectrophotographic processes and is useful in automatic xerographicequipment.

This invention relates in general to imaging systems and, moreparticularly, to improved imaging materials, their manufacture and use.

The formation and development of images on the surface ofphotoconductive materials by electrostatic means is well known. Thebasic xerographic process, as taught by C. F. Carlson in U.S. Patent2,297,691, involves placing a uniform electrostatic charge on aphotoconductive insulating layer, exposing the layer to a light andshadow image to dissipate the charge on the areas of the layer exposedto the light and developing the resulting latent electrostatic image bydepositing on the image a finelydivided electroscopic material referredto in the art as toner. The toner will normally be attracted to thoseareas of the layer which retain a charge, thereby forming a toner imagecorresponding to the latent electrostatic image. This powder image maythen be transferred to a support surface such as paper. The transferredimage may subsequently be permanently affixed to the support surface asby heat. Other suitable fixing means such as solvent or overcoatingtreatment may be substituted for the foregoing heat fixing steps. Manymethods are known for applying the electroscopic particles to the latentelectrostatic images to be developed. One development method asdisclosed by E. N. Wise in U.S. Patent 2,618,552 is known as cascadedevelopment. In this method, develop er material comprising relativelylarge carrier particles having finely-divided toner particleselectrostatically clinging to the surface of the carrier particles isconveyed to and rolled or cascaded across the latent electrostaticimage-bearing surface. The composition of the toner particles is sochosen as to have a triboelectric polarity opposits that of the carrierparticles. As the mixture cascades or rolls across the image-bearingsurface, the toner particles are electrostatically deposited and securedto the charged portions of the latent image and are not deposited on theuncharged or background portions of the image. Most of the tonerparticles accidentally deposited in the background are removed by therolling carrier, due apparently, to the greater electrostatic attractionbetween the toner and the carrier than between the toner and thedischarged background. The carrier particles and unused toner particlesare then recycled. This technique is extremely good for the developmentof line copy images. The cascade development process is the most widelyused commercial xerographic development technique. A general purposeoflfice copying machine incorporating this technique is described inU.S. Patent 3,099,943.

Another technique for developing electrostatic images is the magneticbrush process as disclosed, for example, in U.S. Patent 2,874,063. Inthis method, a developer "ice material containing toner and magneticcarrier particles is carried by a magnet. The magnetic field of themagnet causes alignment of the magnetic carriers in a brush-likeconfiguration. This magnetic brush is engaged with an electrostaticimage-bearing surface and the toner particles are drawn from the brushto the electrostatic image by electrostatic attraction. Many othermethods are known for applying electroscopic particles to the latentelectrostatic image to be developed. These methods include: powder clouddevelopment, touchdown development and liquid development as describedin U.S. Patents 2,221,776; 2,895,847; and 2,891,911, respectively. Theprocesses as mentioned above together with numerous variations are wellknown to the art through various patents and publications and throughthe wide spread availability and utilization of electrostatographicimaging equipment.

In automatic xerographic equipment, it is conventional to employ axerographic plate in the form of a cylindrical drum which iscontinuously rotated through a cycle of sequential operations includingcharging, exposure, developing, transfer and cleaning. The plate isusually charged with corona of positive polarity by means of a coronagenerating device of the type disclosed by L. E. Walkup in U.S. Patent2,777,957 which is connected to a suitable source of high potential.After forming a powder image on the electrostatic latent image duringthe development step, the powder image is electrostatically transferredto a support surface by means of a corona generating device such as thecorona device mentioned above. In automatic equipment employing arotating drum, a support surface to which a powdered image is to betransferred is moved through the equipment at the same rate as theperiphery of the drum and contacts the drum in the transfer positioninterposed between the drum surface and the corona generating device.Transfer is effected by the corona generating device which imparts anelectrostatic charge to attract the powder image from the drum to thesupport surface. The polarity of charge required to effect imagetransfer is dependent upon the visual form of the original copy relativeto the reproduction and the electroscopic characteristics of thedeveloping material employed to effect development. For example, where apositive reproduction is to be made of a positive original, it isconventional to employ a positive polarity corona to effect transfer ofa negatively charged toner image to the support surface. When a positivereproduction from a negative original is desired, it is conventional toemploy a positively charged developing material which is repelled by thecharged areas on the plate to the discharged areas thereon to form apositive image which may be transferred by negative polarity corona. Ineither case, a residual powder image usually remains on the plate aftertransfer. Because the plate may be reused for a subsequent cycle, it isnecessary that the residual image be removed to prevent ghost imagesfrom forming on subsequent copies. In the positive-to-positivereproduction process described above, the residual developer powder istightly retained on the plate surface by a phenomenon that is not fullyunderstood but believed caused by an electric charge that preventscomplete transfer of the powder to a support surface, particularly inthe image areas. The charge is substantially neutralized by means2,832,977. The brush type cleaning means usually comprises one or morerotating brushes which brush residual powder from the plate into astream of air which is exhausted through a filtering system. A typicalweb cleaning device is disclosed by W. P. Graif, Jr., et al. in US.Patent 3,186,838. As disclosed by Graff, Jr., et al., removal of theresidual powder on the plate is effected by rubbing a web of fibrousmaterial against the plate surface. These inexpensive and disposablewebs of fibrous material are advanced into pressure and rubbing orwiping contact with the imaging surface and are gradually advanced topresent a clean surface to the plate whereby substantially completeremoval of the residual powder from the plate is effected.

While ordinarily capable of producing good quality images, conventionaldeveloping systems suffer serious deficiencies in certain areas. Theelectrical and transfer characteristics of electrostatic imagingsurfaces are adversely affected when relative humidity is high. Becauseof the influence of various forces such as electrostatic and van derWaal forces, many toner particles tend to formadherent unwanted depositswhich impair proper cleaning of reusable imaging plates, belts or drums.Numerous known carriers are abrasive in nature. Abrasive contact betweentoner particles, carriers, and imaging surfaces, accelerates mutualdeterioration of these components. Rubbing contact between cleaningdevices and the imaging surface also results in rapid erosion of theimaging surfaces. Frequent replacement of carriers and imaging plates isexpensive, inconvenient and time consuming. Fines formed from theattrition of toner on rough imaging surfaces tend to drift and formunwanted deposits on critical machine parts. Electrostatographic copiesshould possess good line image contrast as well as acceptable solid areacoverage. However, when a process is designed to improve either lineimage contrast or solid area coverage, reduced quality of the other canbe expected. Attempts to increase image density by depositing greaterquantities of toner particles on the latent electrostatic image areusually rewarded with an undesirable increase in background deposits.Further, for reasons not fully understood, image quality is oftenimpaired by the appearance of powder deficient spots in the powderimage. Although the present selenium xerographic plates possess goodtemperature stability, the vitreous selenium layer tends to crystallizeunder high temperature conditions with attendant degradation of imagingqualities. In addition, difliculty is often encountered in maintaining agood bond between vitreous selenium layers and conductive substrates,particularly where the conductive substrates are flexible. Thus, thereis a continuing need for a better system for developing latentelectrostatic images.

It is, therefore, an object of this invention to provide a system whichovercomes the above noted deficiencies.

It is another object of this invention to improve the adhesion ofselenium layers to conductive substrates.

It is a further object of this invention to provide electrophotographicplates having stable electrical properties.

-It is a still further object of this invention to provideelectrophotographic plates which enhance the transfer of toner particlesin background areas of imaged surfaces to carriers.

It is another object of this invention to provide an electrophotographicplate from which toner particles are easily removed by cleaning devices.

It is still another object of this invention to provideelectrophotographic plates which are resistant to mechanical abrasion.

It is a further object of this invention to provide electrophotographicplates which promote the formation of dense transferred toner images.

It is a still further object of this invention to provide anelectrophotographic plate which reduces or eliminates powder deficientspots.

It is another object of this invention to provide an electrophotographicplate having physical and chemical properties superior to those of knownelectrophotographic plates.

The above object and others are accomplished, generally speaking, byproviding a photoconductor formed by condensing the co-evaporated vaporsof selenium compositions and a hydrophobic metal salt of a fatty acidhaving a melting point of from about 30 C. to about C. on a substrate.The condensed vapors of the components appear to be randomly mixed toform a continuous film on the substrate. These films may be formed inany convenient thickness. Although thicknesses of several hundredangstroms may be formed, films ranging from about 1,000 angstroms toabout microns, are preferred for photoconductive applications.Satisfactory results are obtained with photoconductive layers comprisingup to about 20 percent, based on the weight of the ultimate mixture, ofthe metal salt. Optimum results are obtained when the photoconductivelayer contains about 2 percent to about 5 percent of the metal salt.Although the initial electrostatic imaging surface potential may bereduced and abrasion resistance improved when the proportion of metalsalt present is increased above about 20 percent, undesirable backgrounddeposits increase noticeably. If the charge voltage is reduced tocompensate for the presence of zinc stearate in excess of about 20percent, the images begin to acquire a washed out appearance. When lessthan about 0.1 percent metal salt based on the total weight of thephotoconductive layer is employed, the abrasion resistance, transfercharacteristics and image forming properties are substantially the sameas a photoconductive layer which does not contain the metal salt.

Although the initial deposit on the substrate may contain both thephotoconductive component and the metal salt, it is preferred thatvaporation of the selenium photoconductor component be initiated priorto vaporization of the metal salt. This embodiment is preferred becausea greater surface area of photoconductive selenium material is presentedfor electrical contact with the conductive substrate. Further,initiation of selenium photoconductor evaporation prior to vaporizationof the metal salt prevents the less desirable occurrence of a continuousfilm of metal salts on the surface of the conductive substrate prior todeposition of the selenium photoconductive material. The formation of acontinuous metal salt film on the conductive substrate prior todeposition of any selenium photoconductive material is undesirable,because it tends to insulate the selenium photconductive material fromthe conductive substrate and also reduces adhesion of the seleniumphotoconductive material to the substrate.

The photoconductive films of this invention may be formed on anysuitable conductive substrate. Typical conductive substrates includebrass, aluminum, gold, platinum, steel, glass coated with conductiveoxides, metallized paper, laminated sheets of metal and plastic and thelike. The conductive substrate may be in the form of a fiat plate,cylinder, flexible sheet or any other suitable configuration.

Excellent results are obtained with zinc stearate. However, any suitablestable solid hydrophobic metal salt of a fatty acid having a meltingpoint greater than about 30 C. may be substituted for zinc stearate. Themetal salts should be substantially insoluble in water. Photoconductiveplates containing water soluble metal salts lack the proper electricalproperties and are adversely affected by humidity changes normallyoccurring in the ambient atmosphere. A great many salts commonlyregarded as insoluble, actually dissolve to a slight extent. Toeffectively carry out the purposes of this invention, the watersolubility of the salt should be negligible. The salts having thedesired specific characteristics include many salts of saturated fattyacids, unsaturated fatty acids, partially hydrogenated fatty acids,substituted fatty acids and mixtures thereof. Typical fatty acids fromwhich stable solid hydrophobic metal salts may be derived include:caproic acid, enanthlic acid, caprylic acid, pelargonic acid, capricacid, undecylic acid, lauric acid, tridecoic acid, myristic acid,pentadecanoic acid, palmitic acid, mergaric acid, stearic acid,nondecyclic acid, arachidic acid, behenic acid, stillingic acid,palmitoleic acid, oleic acid, ricinoleic acid, petroselinic acid,vaccenic acid, linoleic acid, linolenic acid, eleostearic acid, licanicacid, parinaric acid, gadoleic acid, arachidonic acid, cetoleic acid andmixes thereof. Typial stable solid metal salts of fatty acid include:barium stearate, lead stearate, iron stearate, nickel stearate, cobaltstearate, copper stearate, strontium stearate, calcium stearate, cadmiumstearate, magnesium stearate, zinc oleate, manganese oleate, ironoleate, cobalt oleate, copper oleate, lead oleate, magnesium oleate,zinc palmitate, cobalt palmitate, copper palrnitate, magnesiumpalmitate, aluminum palmitate, calcium palmitate, lead caprylate, leadcaproatae, zinc linoleate, cobalt linoleate, calcium linoleate, zincricinoleate, cadmium ricinoleate, and mixtures thereof.

Optimum results are obtained when the photoconductive layer contains themetal salt and selenium. However, photoconductvie mixtures, alloys orcompounds of selenium with another material such as tellurium andarsenic may be substituted for selenium.

The advantages of this method will become further apparent uponconsideration of the following disclosure of the invention, particularlywhen taken in conjunction with the accompanying drawing wherein anembodiment of an apparatus for preparing thin films comprising vitreousselenium and a solid hydrophobic metal salt of a fatty acid isillustrated.

In the drawing, bell jar is supported by a plate 12 containing vacuumlines 14 and control valve 16. Resistance heating wires 18 and 20 areemployed to heat crucibles 22 and 24, respectively. A rod 26 is employedto support a fluid cooled platen 28. The fluid cooled platen 28 isprovided with a fluid supply tubes 30. The substrate 32 to be coated ismounted on the lower face of platen 28 by a masking frame 34 secured tothe platen 28 by, for example, screws 36. Supply tubes are shielded fromvapors by plate 38.

The selenium or selenium alloy and the solid hydrophobic metal salt of afatty acid are each placed in separate crucibles composed of inertmaterial such as quartz or other suitable refractory material.

The pressures within bell jar 10 is maintained at a vacuum of about 210* to 2 10- torr. However, a vacuum above or below this range can alsobe employed with satisfactory results. A relatively low substratetemperature such as, for example, from about C. to 90 C. may be employedto condense the vapors. The temperature of the components in crucibles22 and 24 are maintained at a temperature between about their meltingpoints and their boiling points. Thus, for example, in forming aselenium zinc stearate photoconductive film containing about 98 percent,by weight, selenium and about '2 percent, by weight, zinc stearate, atemperature of about 217 C. for the selenium and about 130 C. for thezinc stearate is satisfactory. When a larger proportion of selenium inthe film is desired, the temperature of the crucible containing seleniumshould be increased and/or the temperature of the crucible containingzinc stearate reduced. To increase the relative quantity of zincstearate in the photoconductive film, the above described temperatureregulation is reversed.

Under the above conditions, a film thickness of about 5 to about 30microns is obtained for deposition periods ranging from about 1 to about3 hours at a vacuum of about 2 10* torr. In view of the above describedprocedure, it is apparent that the amount of a particular component inthe photoconductive film is primarily dependent upon the temperatureemployed to vaporize each of the components at a given pressure.

The unexpectably better results obtained by co-evaporating a solidhydrophobic metal salt of a fatty acid with selenium or selenium alloysmay be due to many factors. For example, it is postulated that theslippery metal salt material reduces friction during the development andcleaning processes; reduces the attraction of toner particles to theimaging surface during image transfer thereby improving print density;provides at least a partially Waterproof photoconductor surface whichpermits electrical stability under varying humidity conditions; and isconstantly brought to the surface of the photoconductor throughout thelife of the photoconductor layer as the photoconductor layer is slowlyworn away during use.

Although specific materials and conditions are set forth in the aboveexamples, these are merely illustrative of the present invention.Various other compositions such as the typical materials listed aboveand various conditions when suitable may be substituted for those givenin the examples with similar results. The photoconductive layer of thisinvention may contain other materials codeposited therewith to enhance,sensitize, synergize or otherwise modify the photoconductive propertiesof the composition.

Many other modifications of the present invention will occur to thoseskilled in the art upon a reading of this disclosure. These are intendedto be encompassed within the spirit of this invention.

The following examples further specifically define and describe theprocess of the present invention for forming photoconductive layerscomprising selenium and a solid hydrophobic metal salt of a fatty acid.Parts and percentages are by weight unless otherwise indicated. Theexamples below are intended to illustrate the various preferredembodiments of carrying out the invention.

EXAMPLE I Two quartz crucibles are charged with finely-divided ballmilled selenium and zinc stearate, respectively. These crucibles areplaced in resistance heaters positioned in a vacuum chamber similar tothe chamber illustrated in the drawing. The vacuum chamber is evacuatedto a vacuum of about 2 10- torr. A brass substrate is Secured to a watercooled platen located about 12 inches above the quartz crucibles andmaintained at a temperature of about 54 C. The selenium and zincstearate are then evaporated onto the brass plate surface by maintainingthe temperature of the selenium crucible at about 217 C. and the zincstearate crucible at about C. by means of the resistance heatingelements. These conditions are maintained for about 2 /2 hours at whichtime vaporation is terminated. After the vacuum chamber is cooled toroom temperature and the vacuum broken, the coated brass plate isremoved from the chamber. No crystallinity is detected in the depositedfilm when examined by X-ray diffraction.

EXAMPLE II The procedure described in Example I is repeated eX- ceptthat no zinc stearate is employed. The resulting photoconductive plateis compared to the photoconductive plate of Example I by utilizing eachof the plates in a xerographic copying process in the following manner.Each photoconductive plate is corona charged to a voltage of about 600volts and exposed to identical light and shadow patterns to form alatent electrostatic image on their surfaces. The latent images are thendeveloped by cascading a mixture of colored polystyrene copolymer tonerparticles having an average particle size of about 10 to about 20microns and 99 parts coated carrier particles having an average particlesize of about 600 microns across the surface bearing the latent image.The image is then transferred to a sheet of paper and heat fused 7thereon to render it permanent. Both copies possess sharp line contrastbut the copy produced with the photoconductive plate containing zincstearate possessed higher density solid area coverage and cleanerbackground than the copy produced with the zinc stearate freephotoconductive plate.

EXAMPLE III The procedure employed in Example I is repeated with calciumstearate substituted for zinc stearate. The resulting photoconductiveplate is corona charged to a voltage of about 600 volts and exposed to alight and shadow pattern to form a latent electrostatic image on itssurface. The latent image is then developed by cascading a mixture ofcolored polystyrene copolymer toner particles having an average particlesize of about 10 to about 20 microns and 99 parts coated carrierparticles having an average particle size of about 600 microns acrossthe surface bearing the latent image. The resulting powder image is thentransferred to a sheet of paper and heat fused thereon to render itpermanent. This copy is compared to the copy obtained with the salt-freeselenium plate described in Example II. The copy obtained with thecalcium stearate plate possessed higher density solid area coverage andcleaner background than the copy produced with the salt-freephotoconductive plate described in Example II.

EXAMPLE IV The procedure employed in Example I is repeated with bariumlaurate substituted for zinc stearate. The resulting photoconductiveplate is corona charged to a voltage of about 600 volts and exposed to alight and shadow pattern to form a latent electrostatic image on itssurface. The latent image is then developed by cascading a mixture ofcolored polyethylene toner particles having an average particle size ofabout to about 15 microns and 95 parts coated carrier particles havingan average particle size of about 400 microns across the surface bearingthe latent electrostatic image. The resulting powder image is thentransferred to a sheet of paper and heat fused thereon to render itpermanent. This copy is compared to the copy obtained with the salt-freeselenium plate described in Example II. The copy obtained With thebarium laurate plate possessed higher density solid area coverage andcleaner background than the copy produced with the saltfreephotoconductive plate described in Example II.

EXAMPLE V Two molybdenum crucibles are charged with finelydividedmixture of about 95 parts selenium and about 5 parts arsenic trisulfideand zinc stearate, respectively. These crucibles are placed inresistance heaters positioned in a vacuum chamber similar to the chamberillustrated in the drawing. The vacuum chamber is evacuated to a vacuumof about 2 10 torr. An aluminum substrate is secured to a water cooledplaten located about 4 inches above the molybdenum crucibles andmaintained at a temperature of about 80 C. The selenium, arsenictrisulfied and zinc stearate are then evaporated onto the aluminumsurface by maintaining the temperature of the crucible containing themixture of selenium and arsenic trisulfied at about 220 C. and thecrucible containing zinc stearate at about 130 C. by means of theresistance heating elements. These conditions are maintained for about0.5 hour at which time vaporization is terminated. After the vacuumchamber is cooled to room temperature and the vacuum broken, the brassplate is removed from the chamber. No crystallinity is detected in thedeposited film when examined by X-ray def-fraction.

EXAMPLE VI The procedure described in Example V is repeated except thatno zinc stearate is employed. The resulting photoconductive plate iscompared to the photoconductive plate of Example V by utilizing each ofthe plates in a xerographic copying process in the following manner.

Each photoconductive plate is corona charged to a voltage of about 600volts and exposed to identical light and shadow patterns to form alatent electrostatic lmage on their surfaces. The latent images are thendeveloped by cascading a mixture of colored polystyrene copolymer tonerparticles having an average particle size of about 10 to about 20microns and 99 parts coated carrier particles having an average particlesize of about 600 mlcrons across the surface bearing the latent image.The image [5 then transferred to a sheet of paper and heat fused thereonto render it permanent. Both copies possess sharp line contrast but thecopy produced with the photoconductive plate containing zinc stearatepossess higher density SOlld area coverage and cleaner background thanthe copy p oduced with the photoconductive plate which did not containzinc stearate.

EXAMPLE VII The procedure employed in Example V is repeated with zincoleate substituted for zinc stearate. The resulting photoconductiveplate is corona charged to a voltage of about 600 volts and exposed to alight and shadow pattern to form a latent electrostatic image on itssurface. The latent image is then developed by cascading a mixture ofcolored polystyrene copolymer toner particles having an average particlesize of about 10 to about 20 microns and 99 parts coated carrierparticles having an average particle size of about 600 microns acrossthe surface bearing the latent image. The resulting powder image is thentransferred to a sheet of paper and heat fused thereon to render itpermanent. This copy is compared to the copy obtained with the salt-freephotoconductive plate described in Example VI. The copy obtained withthe zinc oleate plate possessed higher density solid area coverage andcleaner background than the copy produced with the salt-freephotoconductive plate.

EXAMPLE VIII The procedure described in Example II is repeated exceptthat the xerographic copying process is conducted in a chambermaintained at about F. and about 80 percent relative humidity. Both thedeveloping material and the two plates are maintained within thehumidity chamber at 80 F. and about 80 percent relative humidity forapproximately 20 hours immediately prior to utilizing each of the platesin a xerographic copying process. The copies produced with thestearate-free photoconductive plate possess good good line contrast butpoor solid area coverage. Copies produced with the plate containing zincstearate possess excellent line contrast and very good solid areacoverage.

EXAMPLE IX The zinc stearate free and zinc stearate treated platesdescribed in Example II are subjected to about 10,000 imaging cycles;each cycle comprising a charging step, an exposure step, a developingstep and a transfer step as described in Example II. A cleaning step isalso included in the cycle and comprises Wiping the surface of plateswith cotton to remove any residual toner material which is not removedduring the transfer step. Micrograph studies of the imaging surfaces ofthe plates reveal substantially less wear and a greatly fewer number ofdeep scratches in the zinc stearate treated plate than in the untreatedplate.

EXAMPLE X EXAMPLE Ix The zinc oleate free and zinc oleate treated platesdescribed 111 Example VII are subjected to about 10,000

imaging cycles; each cycle comprising the steps described in Example IX.Micrograph studies of the imaging surfaces of the plates reveal reducedwear and fewer scratches in the zinc oleate treated plate than in theuntreated plate.

The expression electrophotographic plate as employed herein is intendedto include fiat plates, cylinders and continuous belts.

Although specific components, proportions and procedures have beenstated in the above description of the preferred embodiments of thenovel treatment system, other suitable materials, as listed above, maybe used with similar results. Further, other materials and proceduresmay be employed to synergize, enhance or otherwise modify the novelsystem. Other modifications and ramifications of the present inventionwill appear to those skilled in the art upon a reading of thedisclosure. These are intended to be included within the scope of thisinvention.

What is claimed is:

1. A process for the production of an electrophotographic plate whichcomprises:

(a) simultaneously heating a photoconductive material selected from thegroup consisting of selenium, selenium compounds and selenium alloys anda solid hydrophobic metal salt of a fatty acid under vacuum conditionsto form vapors of said photoconductive material and said solidhydrophobic metal salt of a fatty acid and (b) simultaneously condensingthe vapors of said photoconductive material and said hydrophobic metalsalt of a fatty acid onto a cold conductive substrate maintained at atemperature below the melting point of said photoconductive material andsaid solid hydrophobic metal salt of a fatty acid whereby a continuousphotoconductive layer is formed on said substrate.

2. A process for the production of an electrophotographic plateaccording to claim 1 including initiating vaporization of saidphotoconductive material prior to coevaporization of saidphotoconductive material and said solid hydrophobic metal salt of afatty acid whereby at least a portion of said vaporized photoconductivematerial is deposited on said cold conductive substrate prior todeposition of said solid hydrophobic metal salt of a fatty acid.

3. An electrophotographic plate comprising a photoconductive layer on asupporting conductive substrate, said layer comprising a photoconductivematerial selected from the group consisting of selenium, seleniumcompounds and selenium alloys and a solid hydrophobic metal salt of afatty acid.

4. An electrophotographic plate according to claim 3 wherein saidphotoconductive layer comprises from about 99.9 to about parts by weightof said photoconductive material and from about 0.1 to about 20 parts byweight of said solid hydrophobic metal salt of a fatty acid.

5. An electrophotographic plate according to claim 3 wherein said solidhydrophobic metal salt of a fatty acid is zinc stearate.

6. An electrophotographic plate according to claim 3 wherein said layercomprises a greater concentration of said photoconductive materialadjacent said supporting conductive substrate than elsewhere in saidphotoconductive layer.

7. A process for forming a latent electrostatic charge pattern on asurface including the steps of providing an electrophotographic platecomprising a photoconductive layer on a supporting conductive substrate,said layer comprising a photoconductive material selected from the groupconsisting of selenium, selenium compounds and selenium alloys and asolid hydrophobic metal salt of a fatty acid, uniformlyelectrostatically charging said photoconductive layer, and exposing saidphotoconductive layer to a pattern of activating electromagneticradiation to thereby form a latent electrostatic image on saidphotoconductive layer.

8. An electrophotographic imaging process including the steps ofproviding an electrophotographic plate comprising a photoconductivelayer on a supporting substrate, said layer comprising a photoconductivematerial selected from the group consisting of selenium and seleniumalloys and a solid hydrophobic metal salt of a fatty acid,electrostatically charging said photoconductive layer, exposing saidlayer to an electromagnetic image pattern to be reproduced to therebyform a latent electrostatic image on said photoconductive layer, anddeveloping said latent electrostatic image with electroscopic mark-' ingparticles.

References Cited UNITED STATES PATENTS 3,329,499 7/1967 Garrett ct al.96-1 3,376,134 4/1968 Stahly et a1 961.8 3,434,832 3/1969 Joseph et al.961.5

GEORGE F. LESMES, Primary Examiner J. C. COOPER, Assistant Examiner Us.01. X.R. 9 -4, 1.4; 117 17.5, 106, 129, 200, 201, 252 501

